The present invention relates to a cooking appliance having a photosensor which detects the presence of an object placed within its cooking compartment.
A prior microwave oven is disclosed in Japanese laid-open Patent Application 4-10389. In the disclosed microwave oven, a photosensor including a light emitter, such as a LED, and a light receiver, using a phototransistor, is provided on a side wall of its cooking compartment. The photosensor detects whether the light receiver is illuminated with light from the light emitter. A microcomputer determines the height of food in the cooking compartment and presence of any attachment used in cooking, such as an oven plate for oven cooking or a turntable for microwave cooking, based on the output of the photosensor.
For example, if no turntable is present, the light receiver can receive light- from the light emitter through the cooking compartment. More specifically, the light emitter generates light in a single pulse. The microcomputer determines whether a voltage, generated by the light receiver in response to detecting light, exceeds a predetermined voltage. If the voltage is lower than the predetermined voltage, the microcomputer determines that the turntable is in the cooking compartment, and microwave cooking is desired. If the voltage is higher than the predetermined voltage, the microcomputer determines the turntable is not in the cooking compartment, and oven cooking is desired. The microwave oven automatically cooks food based on the determination of the microcomputer.
When the light receiver is illuminated, however, the microcomputer sometimes fails to detect the presence of the turntable because the light receiver output is affected by electrical or optical noise. When the photosensor also detects the size of food in the compartment, a similar problem can occur. These failures can cause an erroneous mode of cooking.